1. Field of the Invention
The present invention relates to apparatus for making printing masters used, for example, in general printing and textile printing.
2. Description of the Prior Art
In natural color and multi-color photographic printing and plate-making, it is the general practice that an original pattern is decomposed into three print patterns in three primary colors or into four print patterns including a monochromatic pattern in addition to the three primary color patterns. The desired color tone is reproduced by superimposedly printing these patterns on an object. In textile printing, there have been difficulties in reproducing the desired color tone by simply superimposing a set of print patterns on an object cloth, chiefly due to the dye or pigment used. This has made it impossible to use the three primary colors. Hence, in multi-color printing for a pattern comprising, for example, five colors, the provision of five printing masters, constructed by decomposing an original pattern, has been indispensable.
Recently, the decomposition of an original tone has been achieved by a mechanical process using a color decomposing apparatus, which normally comprises more than three photoelectric systems depending upon the number of colors to be detected for color tone decomposition. FIG. 1 schematically illustrates an example of a conventional color decomposing apparatus (with only one photoelectric system shown for explanatory simplicity).
Referring to FIG. 1, the numeral 1 denotes a first rotary cylinder on which a pattern original 2 is wound. The numeral 3 denotes a second rotary cylinder which is synchronous with the cylinder 1 when rotated and on which a recording object 4 such as a photosensitive film or a photosensitive copper plate is wound. The numeral 5 denotes an illumination lamp and 6 a projection lens for converging the light from the lamp 5 and thus illuminating a given point on the original 2. The numeral 7 denotes an optical system for detecting color components from the light reflected from the original 2, and 8 is a photoelectric transducer element, such as a phototransistor and a photoelectric electron - multiplier tube, for transducing the decomposed light into an electric signal. The numeral 100 stands for a detecting system which comprises the illumination lamp 5, the projection lens 6, the optical system 7, and the photoelectric transducer element 8. The numeral 9 denotes an amplifier, 10 a wave shaping circuit, 11 a drive amplifier, 12 a crater tube, such as an electro-optic transducer element for producing light in response to an input signal given, and 13 is a lens for converging the light from the electro-optic transducer element 12. The numeral 101 stands for a reproducing system which comprises the electro-optic transducer element 12, and the lens 13. The detecting system 100 and the reproducing system 101 are moved by a drive device (not shown) in the rotating axial direction of the rotary cylinders 1 and 3, to thereby make auxiliary scanning on the pattern original 2 and on the recording object 4.
The conventional apparatus of FIG. 1 operates in the following manner. The original 2 which is wound on the rotary cylinder 1 is illuminated with the lamp 5 by way of the projection lens 6. The light reflected from the original 2 is led to the optical system 7 and decomposed into color light components. The decomposed light is transduced into an electrical signal by the photoelectric transducer element 8. The electric signal detected by the detecting device 100 is then amplified by the amplifier 9 shaped by the shaping circuit 10, and then supplied through the drive amplifier 11 to the reproducing device 101 in which the electric signal is transduced into light by the electro-optic transducer element 12. The light is then converged through the lens 13, and applied to the recording object 4 on the rotary cylinder 3. The rotary cylinders 1 and 3 are rotated in the arrow-marked direction by a motor (not shown) to cause the detecting device 100 and the reproducing device 101 to perform main scanning. Also, the detecting device 100 and the reproducing device 101 are moved by a drive device (not shown) in the rotating axial direction of the cylinders 1 and 3 to cause the devices 100 and 101 to perform auxiliary scanning. Consequently, the entire surface of the pattern original 2 is scanned whereby a printing master is formed.
In textile printing, it is to be taken into consideration that the printing object is a cloth which is more or less elastic, and the degree of dye blurring over the cloth varies according to the kind of cloth, the thickening agent used, and the printing method or process employed. To obtain an accurate print reproduction, therefore, the pattern of the master is made smaller than that of the original by an amount of estimated dye blurring (or a "bleed allowance"), or is made slightly larger than that of the original by an amount of pattern overlap (or an "overlap allowance") thereby preventing the boundary between patterns on the cloth from being left undyed. In practical printing, however, while somewhat satisfactory, the conventional color-decomposing apparatus has been far from perfect in making printing masters accurately without depending on human skill.
In roller printing, it should be understood that the size of the printing master should be changed according to the diameter of the engraved roll used in order to realize the complete repeat printing of an original. For this purpose, it is necessary to enlarge or compress the rotary cylinder only in its circumferential direction as shown in FIG. 1. Accordingly, the diameter of the rotary cylinder 1 should be different from that of the rotary cylinder 3. In practice, however, the rotary cylinders 1 and 3 are too heavy to be readily handled in order to change their sizes accurately. Thus, in the prior art conventional apparatus, an accurate printing master could not be realized without dependence upon a photographic process or human skill which would be used to adjust the blur margin or the overlap allowance. However, the use of a photographic process requires the use of films at an intermediate process which is time consuming and expensive. Moreover, the process of manually making the printing master is heavily dependent on the experience skill of a craftsman, which takes a good many years to attain. In addition, it takes this process a considerable length of time to produce a complete printing master, with the result that the production cost rises considerably.